The invention relates to a device for applying unipolar electrical charges by means of an elongated corona electrode with at least one auxiliary electrode to moving, essentially electrically insulating surfaces supported on an electrically conductive counter electrode, and with a high-voltage d.c. source connected to the electrodes.
A device of this kind is known from DE 24 10 479 C3. In the known device, the corona electrode is enclosed and screened by an auxiliary electrode over an angular area of approximately 270.degree., and the edges of the auxiliary electrode which are of decisive importance for the field generation and the tips of the corona electrode are spaced at the same distance from the surface to be charged. The auxiliary electrode is directly connected to ground, to which also the one pole of a high-voltage d.c. source is connected, the other pole of which is connected to the corona electrode.
In the known device, opposing electric fields can easily develop due to the occurrence of an interfering charge, and these can disturb the field directed from the corona electrode towards the surface to be charged and hence the applying of a unipolar electrical charge. In particular, in the case of tip electrodes, there can also be uneven charge distributions on the surface to be charged and the tip electrodes can, so to speak, be "reproduced" in the form of stripes on the moved surface to be charged.